The present invention is concerned with an axial piston machine, pump or hydraulic motor, with a rotary cylinder block having a block end face cooperating with a stationary control face having high pressure and low pressure control ports arranged along a circle having a radius which is smaller than the radius of the circle along which the cylinders are arranged. When the clyinder block end face and the control face of the stationary body are pressed against each other, the cylinder ports and the high pressure and low pressure ports communicate, but a certain leakage is unavoidable.
The U.S. Pat. No. 907,737 discloses an axial piston motor in which the cylinders are arranged along a circle which is greater than the circle along which the inlet and outlet control ports are located. The diameter of the circles of the ports is substantially smaller than the diameter of the circle on which the cylinders are located. Three axially effective adjusting screws hold the stationary and rotary parts together. It is a disadvantage of this motor that the forces acting in the cylinders on the cylinder block have a greater radial distance from the rotor axis than the opposing forces exerted by the ports on the cylinder block. The result is that different opposing moments act on the cylinder block which causes tilting of the cylinder block. When the cylinder block end face is thus tilted relative to the stationary control face, great leakage occurs. The leakage can be somewhat reduced by tightening the adjusting screws which press the cylinder block against the control face of the stationary body, but the friction between the engaging faces is increased, and the efficiency reduced.
The German A.S. 1,285,891 discloses apparatus for hydraulically pressing the stationary body with its control face against the cylinder block end face of an axial piston machine. In this machine, the ports are also arranged along a smaller circle than the cylinders so that a tilting moment acts on the cylinder block. The sealing between the cylinder block end face and the stationary control face is improved by providing a piston shaped projection on the side of the stationary body remote from the cylinder block, which moves in a corresponding cylinder receiving fluid under pressure so that the stationary body with its control face is pressed into sealing contact with the cylinder body end face. This construction has the same disadvantage as the other described machine according to the prior art, since stable running of the rotor can be obtained only by increasing the axial pressure which causes undesirable friction and wear.